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168 lines
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<html lang="en">
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<head>
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<title>Miscellaneous Commands - Untitled</title>
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<meta name="description" content="Untitled">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Simple-Commands.html#Simple-Commands" title="Simple Commands">
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<link rel="prev" href="REGION_005fALIAS.html#REGION_005fALIAS" title="REGION_ALIAS">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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This file documents the GNU linker LD
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(GNU Toolchain for the A-profile Architecture 9.2-2019.12 (arm-9.10))
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version 2.33.1.
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Copyright (C) 1991-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled ``GNU Free Documentation License''.-->
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<style type="text/css"><!--
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Miscellaneous-Commands"></a>
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<p>
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Previous: <a rel="previous" accesskey="p" href="REGION_005fALIAS.html#REGION_005fALIAS">REGION_ALIAS</a>,
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Up: <a rel="up" accesskey="u" href="Simple-Commands.html#Simple-Commands">Simple Commands</a>
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<hr>
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</div>
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<h4 class="subsection">3.4.5 Other Linker Script Commands</h4>
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<p>There are a few other linker scripts commands.
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<dl>
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<dt><code>ASSERT(</code><var>exp</var><code>, </code><var>message</var><code>)</code><dd><a name="index-ASSERT-422"></a><a name="index-assertion-in-linker-script-423"></a>Ensure that <var>exp</var> is non-zero. If it is zero, then exit the linker
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with an error code, and print <var>message</var>.
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<p>Note that assertions are checked before the final stages of linking
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take place. This means that expressions involving symbols PROVIDEd
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inside section definitions will fail if the user has not set values
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for those symbols. The only exception to this rule is PROVIDEd
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symbols that just reference dot. Thus an assertion like this:
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<pre class="smallexample"> .stack :
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{
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PROVIDE (__stack = .);
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PROVIDE (__stack_size = 0x100);
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ASSERT ((__stack > (_end + __stack_size)), "Error: No room left for the stack");
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}
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</pre>
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<p>will fail if <code>__stack_size</code> is not defined elsewhere. Symbols
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PROVIDEd outside of section definitions are evaluated earlier, so they
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can be used inside ASSERTions. Thus:
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<pre class="smallexample"> PROVIDE (__stack_size = 0x100);
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.stack :
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{
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PROVIDE (__stack = .);
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ASSERT ((__stack > (_end + __stack_size)), "Error: No room left for the stack");
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}
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</pre>
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<p>will work.
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<br><dt><code>EXTERN(</code><var>symbol</var> <var>symbol</var><code> ...)</code><dd><a name="index-EXTERN-424"></a><a name="index-undefined-symbol-in-linker-script-425"></a>Force <var>symbol</var> to be entered in the output file as an undefined
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symbol. Doing this may, for example, trigger linking of additional
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modules from standard libraries. You may list several <var>symbol</var>s for
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each <code>EXTERN</code>, and you may use <code>EXTERN</code> multiple times. This
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command has the same effect as the ‘<samp><span class="samp">-u</span></samp>’ command-line option.
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<br><dt><code>FORCE_COMMON_ALLOCATION</code><dd><a name="index-FORCE_005fCOMMON_005fALLOCATION-426"></a><a name="index-common-allocation-in-linker-script-427"></a>This command has the same effect as the ‘<samp><span class="samp">-d</span></samp>’ command-line option:
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to make <samp><span class="command">ld</span></samp> assign space to common symbols even if a relocatable
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output file is specified (‘<samp><span class="samp">-r</span></samp>’).
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<br><dt><code>INHIBIT_COMMON_ALLOCATION</code><dd><a name="index-INHIBIT_005fCOMMON_005fALLOCATION-428"></a><a name="index-common-allocation-in-linker-script-429"></a>This command has the same effect as the ‘<samp><span class="samp">--no-define-common</span></samp>’
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command-line option: to make <code>ld</code> omit the assignment of addresses
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to common symbols even for a non-relocatable output file.
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<br><dt><code>FORCE_GROUP_ALLOCATION</code><dd><a name="index-FORCE_005fGROUP_005fALLOCATION-430"></a><a name="index-group-allocation-in-linker-script-431"></a><a name="index-section-groups-432"></a><a name="index-COMDAT-433"></a>This command has the same effect as the
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‘<samp><span class="samp">--force-group-allocation</span></samp>’ command-line option: to make
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<samp><span class="command">ld</span></samp> place section group members like normal input sections,
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and to delete the section groups even if a relocatable output file is
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specified (‘<samp><span class="samp">-r</span></samp>’).
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<br><dt><code>INSERT [ AFTER | BEFORE ] </code><var>output_section</var><dd><a name="index-INSERT-434"></a><a name="index-insert-user-script-into-default-script-435"></a>This command is typically used in a script specified by ‘<samp><span class="samp">-T</span></samp>’ to
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augment the default <code>SECTIONS</code> with, for example, overlays. It
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inserts all prior linker script statements after (or before)
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<var>output_section</var>, and also causes ‘<samp><span class="samp">-T</span></samp>’ to not override the
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default linker script. The exact insertion point is as for orphan
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sections. See <a href="Location-Counter.html#Location-Counter">Location Counter</a>. The insertion happens after the
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linker has mapped input sections to output sections. Prior to the
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insertion, since ‘<samp><span class="samp">-T</span></samp>’ scripts are parsed before the default
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linker script, statements in the ‘<samp><span class="samp">-T</span></samp>’ script occur before the
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default linker script statements in the internal linker representation
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of the script. In particular, input section assignments will be made
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to ‘<samp><span class="samp">-T</span></samp>’ output sections before those in the default script. Here
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is an example of how a ‘<samp><span class="samp">-T</span></samp>’ script using <code>INSERT</code> might look:
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<pre class="smallexample"> SECTIONS
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{
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OVERLAY :
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{
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.ov1 { ov1*(.text) }
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.ov2 { ov2*(.text) }
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}
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}
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INSERT AFTER .text;
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</pre>
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<br><dt><code>NOCROSSREFS(</code><var>section</var> <var>section</var><code> ...)</code><dd><a name="index-NOCROSSREFS_0028_0040var_007bsections_007d_0029-436"></a><a name="index-cross-references-437"></a>This command may be used to tell <samp><span class="command">ld</span></samp> to issue an error about any
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references among certain output sections.
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<p>In certain types of programs, particularly on embedded systems when
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using overlays, when one section is loaded into memory, another section
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will not be. Any direct references between the two sections would be
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errors. For example, it would be an error if code in one section called
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a function defined in the other section.
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<p>The <code>NOCROSSREFS</code> command takes a list of output section names. If
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<samp><span class="command">ld</span></samp> detects any cross references between the sections, it reports
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an error and returns a non-zero exit status. Note that the
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<code>NOCROSSREFS</code> command uses output section names, not input section
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names.
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<br><dt><code>NOCROSSREFS_TO(</code><var>tosection</var> <var>fromsection</var><code> ...)</code><dd><a name="index-NOCROSSREFS_005fTO_0028_0040var_007btosection_007d-_0040var_007bfromsections_007d_0029-438"></a><a name="index-cross-references-439"></a>This command may be used to tell <samp><span class="command">ld</span></samp> to issue an error about any
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references to one section from a list of other sections.
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<p>The <code>NOCROSSREFS</code> command is useful when ensuring that two or more
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output sections are entirely independent but there are situations where
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a one-way dependency is needed. For example, in a multi-core application
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there may be shared code that can be called from each core but for safety
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must never call back.
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<p>The <code>NOCROSSREFS_TO</code> command takes a list of output section names.
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The first section can not be referenced from any of the other sections.
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If <samp><span class="command">ld</span></samp> detects any references to the first section from any of
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the other sections, it reports an error and returns a non-zero exit
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status. Note that the <code>NOCROSSREFS_TO</code> command uses output section
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names, not input section names.
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<br><dt><code>OUTPUT_ARCH(</code><var>bfdarch</var><code>)</code><dd><a name="index-OUTPUT_005fARCH_0028_0040var_007bbfdarch_007d_0029-440"></a><a name="index-machine-architecture-441"></a><a name="index-architecture-442"></a>Specify a particular output machine architecture. The argument is one
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of the names used by the BFD library (see <a href="BFD.html#BFD">BFD</a>). You can see the
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architecture of an object file by using the <code>objdump</code> program with
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the ‘<samp><span class="samp">-f</span></samp>’ option.
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<br><dt><code>LD_FEATURE(</code><var>string</var><code>)</code><dd><a name="index-LD_005fFEATURE_0028_0040var_007bstring_007d_0029-443"></a>This command may be used to modify <samp><span class="command">ld</span></samp> behavior. If
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<var>string</var> is <code>"SANE_EXPR"</code> then absolute symbols and numbers
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in a script are simply treated as numbers everywhere.
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See <a href="Expression-Section.html#Expression-Section">Expression Section</a>.
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</dl>
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</body></html>
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